Biodiesel production in the United States amounted to 105 million gallons in January of 2016 alone. Most of this fuel, however, is not used by consumers in its pure form. Commercial vehicles only infrequently possess engines rated for B100 (that is, 100% biodiesel) consumption. The market for biodiesel is constrained by the percentage of biodiesel for which popular engines are rated. Most commercial and personal vehicles are rated for between 2 and 20 volume percent of biodiesel fuel, with the remainder composed of petrodiesel. The task of producing this blend presently falls to vendors or customers further down the product lifecycle.
Due to these limitations, biodiesel is typically adulterated with conventional petrodiesel to produce dilutions as low as B2. These dilutions are most commonly achieved by simple splash blending, wherein purified B100 and petrodiesel are mixed by the convective motion of pouring both fuels into an on-site vessel. This method has the advantage of simplicity, but suffers from a lack of elegance and efficiency. Splash blending frequently results in incompletely mixed fuel, reducing consumer confidence in biofuel performance. Mechanically agitating large volumes of fluid is expensive, particularly if handled by retail-level vendors that may not be able to justify the price of such an operation. Methods such as in-line blending (injection of B100 into the diesel line servicing a fueling station) has problems with ASTM quality control, as the blend itself is not testable until it is exiting the fuel hose.
Non-catalytic supercritical processes of biodiesel production have become popular because they can handle high water and free fatty acid content. The supercritical conditions of high temperature and pressure be used to catalyze the transesterification reaction. At a high temperature and pressure, methanol and other small alcohols enter a supercritical region. In the supercritical region, the alcohol behaves like a compressible fluid having density intermediate between that of a gas and that of a liquid. Viscosity and surface tension of supercritical methanol is low, allowing excellent mass transfer characteristics. However, the high pressure and high methanol concentration processes of biodiesel production face the problem of energy loss associated with current product purification strategies.
There remains a need for improved methods of separating biodiesel and of making biodiesel blends that overcome the aforementioned deficiencies.